Optical transceivers employ laser packages, such as TOSAs to achieve telecommunication and high speed data communication channels. A standard for optical transceivers, called XFP (10 gigabit small form factor, pluggable) requires that compliant optical transceivers be hot-swappable, protocol independent, and operable at wavelengths of approximately 850, 1310, and 1550 nm in single or multi-mode at nominal data rates of 9.95 G b/s upwards. In telecommunications applications, such transceivers can be used for SONET OC-192 and G.709 “OTU-2”, whilst for data communication they can be used for the transmission of 10 Gb/s optical signals by optical fibre, and 10 Gb/s Ethernet, though the forgoing is not an exhaustive list. The XFP specification was created by the XFP Multi-Source Agreement Group (MSA).
The MSA specification for XFP specifies physical dimensions of both the optical transceiver itself and the cage within which the optical transceiver is received, which cage is mounted on a printed circuit board (PCB). These physical dimension restraints must be borne in mind when the optical transceivers are designed, and act as a limiting feature on the evolution of the circuitry contained within the optical transceiver module. The enclosure for the laser package (e.g. an XFP laser package) is typically elongate with a generally flat walls between a first end with an optical fibre connection and a second end with a projecting arrangement of input/output pins or electrical contacts.
One component of an optical transceiver is a TOSA, which is operable to transmit data via an optical output. A tunable TOSA is one that is controllable to output light at different wavelengths. However, in order to operate more advanced wavelength tunable lasers within a TOSA that have a broad wavelength tuning range, it is necessary to provide the tunable TOSA with additional input channels by which additional control data may be received to select the desired wavelength. These additional input channels complicate compliance with the XFP standard because they necessitate additional connection pins through which the tunable TOSA is connectable to the circuitry of the optical transceiver and because the additional connections to the tunable TOSA increase the physical dimensions thereof. One method of mitigating this issue is the inclusion within the enclosure of a driver IC that is able to translate serialised control data, received from a single data line, into the necessitated multiple parallel control lines required to operate the tunable TOSA. This, however, raises the additional problem of taking up additional space within the enclosure of the TOSA itself. Further, such driver ICs generate heat, which is difficult to remove from within the enclosure.
The present invention seeks to overcome or at least mitigate the aforementioned issues to provide laser packages that maximise the internal volume.